var fhdb1 = document.querySelector("#fhdb");
//console.log(fhdb1);
window.onscroll = function(){
    if (document.documentElement.scrollTop > 100 || document.body.scrollTop > 100){
        fhdb1.style.display = 'block';
    }else {
        fhdb1.style.display = 'none';
    }
};
fhdb1.addEventListener('click', function () {
    window.scrollTo(0,0);
});